Recently, on the basis of the societal demand of resource-saving and energy-saving, a request for a lower fuel consumption of automobiles is growing gradually, and a tire which is excellent in wear resistance, crack growth resistance, etc. is in demand. It is known that it is possible to improve the durability of the tire by stereoregularly controlling the micro structure of rubber components compound to the tire.
On the other hand, it is known that natural rubber has a micro structure where the cis-1,4 bonding amount is 99.7%, and it is recognized that the strain-induced crystallizability is improved due to the high stereoregularity. Regarding the rubber composition using the natural rubber, it may exhibit high durability when used for a tire. On the other hand, it is known that it is also possible to improve the durability by stereoregularly controlling the micro structure of polybutadiene.
It is disclosed in JP2005-530872A (PTL1) that it is possible to synthesize a polybutadiene with a high cis-1,4 bonding amount by using a catalyst system obtained by adding conjugated diene monomer to neodymium compounds. However, a catalyst synthesis process is necessary in order to use the neodymium compounds used in PTL1 as a catalyst. Therefore, problems such as that it is time-consuming to obtain polybutadiene, etc. are still remaining.